The long-term objective of this study is the development of a predictive model for the wear of dental restorative materials. In this application, the fatigue/wear of posterior composite restorative materials is to be investigated. Successful attainment of the project objectives could allow in vitro design and evaluation of new restorative materials without the need for lengthy clinical trials. This should permit the speedier introduction of more effective and cost-efficient materials to the public. The following null hypotheses are to be tested: A. that degree of cure and solvent sorption do not affect the fatigue/wear of a polymer matrix composite; B. that the lifetime predicting/parameters from pin-on-disc fatigue/wear studies are dissimilar from those obtained from shear, bending, and indentation mode fatigue tests; C. that surface morphology of worn and fatigued surfaces is unrelated to wear mechanisms. These specific aims have been designed to aid in testing these hypotheses: 1. To obtain, polymerize to two different degrees of cure, and characterize with respect to glass transition behavior a composite material representative of proprietary dental restorative materials; the material will also be soaked in a water/ethanol solution to simulate exposure to oral fluids. 2. To obtain fatigue data in shear, bending, and indentation modes, and derive the lifetime parameters for these experiments. 3. To employ the pin-on-disc technique to generate fatigue wear in composite samples, and relate these results to those from specific aim 2, as well as to finite element analyses. 4. To develop and refine finite element models of static and dynamic indentation, and crack propagation in particulate reinforced composite materials. 5. To employ morphometric techniques to characterize fatigue/wear surfaces.